1. Field of the Invention
This invention relates to apparatus suitable for optically and directly analyzing one ingredient in a multi-ingredient mixture.
2. Description of the Prior Art
As apparatus for analyzing one of two ingredients as in a case where two materials A and B are mixed to form a material C, a two-wavelength spectrophotometer has been generally known. In this case, a single sample is irradiated by light rays of two different wavelengths, and the ratio of two signals obtained is taken and is thereafter subjected to the logarithmic conversion. In case of measuring the material to-be-measured A in the coexistent material B, two wavelengths .lambda..sub.1 and .lambda..sub.2 at which absorbances by the coexistent material B are equal as shown in FIG. 1 must be selected. By way of example, letting the absorbances of the material A at the wavelengths .lambda..sub.1 and .lambda..sub.2 be a.lambda..sub.1 and a.lambda..sub.2 and those of the material B be b.lambda..sub.1 and b.lambda..sub.2, the concentration of the mixture C becomes as follows: EQU c.lambda..sub.1 = a.lambda..sub.1 + b.lambda..sub.1 ( 1) EQU c.lambda..sub.2 = a.lambda..sub.2 + b.lambda..sub.2 ( 2)
On account of the two-wavelength photometry system, a value to be found becomes as follows: ##EQU1##
Here, the two wavelengths .lambda..sub.1 and .lambda..sub.2 of equal absorbances as to the coexistent material B are selected, so that the following equation holds: EQU b.lambda..sub.2 = b.lambda..sub.1 ( 4)
Therefore, EQU .DELTA.c = a.lambda..sub.2 - a.lambda..sub.1 ( 5)
Accordingly, the influence of the coexistent material is obviated, and one ingredient A can be measured by measuring the mixture C as it is.
With the above method, however, in case where the coexistent material B does not have two wavelengths of equal absorbances as illustrated in FIG. 2, b.lambda..sub.2 .noteq. b.lambda..sub.1, the measurement is impossible. Therefore, the masking of the coexistent material or the pre-treatment of extracting and separating the material to-be-measured is required.
In addition to the foregoing measure, U.S. Pat. No. 3,694,092 has been known. It discloses to the effect that one of mixed ingredients can be simply measured without separation and extraction. Since, however, the two-wavelength photometry system is adopted also in this case, a certain condition is imposed on the selection of the two wavelengths. That is, a wavelength which both the material to-be-measured and the coexistent material absorb must be selected as one of the two wavelengths, and a wavelength which the material to-be-measured does not absorb and which only the coexistent material absorbs must be selected as the other wavelength. Accordingly, although the measurement is possible in case of mixed materials which satisfy the aforecited condition, it becomes impossible in the other case.